The present invention relates to improvements in capacitance-related measurement of fluid pressures, and, in one particular aspect, to unique high-performance absolute-pressure transducers in which widely-different ranges of pressures, such as those near vacuum and at or near atmospheric levels, are advantageously characterized by a single assembly of economical and uncomplicated construction wherein a main diaphragm functions distinctively both as a movable capacitance electrode over one of the ranges and as a means for mechanically inducing variations in a further capacitance array over another range.
It has become common practice to sense and provide related measurements of pressure, and especially very low levels of pressure, in terms of the capacitances exhibited between a pair of closely-spaced electrodes, one of which is adjusted in position relative to the other in accordance with differences in pressures acting upon an associated diaphragm. In the case of so-called "absolute" pressure capacitance manometers, one of the pressures, which is maintained as a reference, is substantially gasless and usually as close to a perfect vacuum as it is feasible and practical to establish and hold on one side of the diaphragm. However, if any such device is to be counted upon to sense and usefully characterize pressures which are very small, its design features, including a relatively close electrode spacing, tend to render it unsuitable for dependable indications of the much larger pressures appearing at or near ambient atmospheric levels. Yet, reliable knowledge about such ambient pressures is commonly quite important to the user, who, among other things, must be able to determine when once-evacuated sensitive systems, monitored precisely while at low pressures, are being brought back up to or near atmospheric levels at which system openings and "dumping" may be ventured safely. It is for such reasons that auxiliary thermocouple-type gages have been used to furnish system operators with at least coarse information about pressures near atmospheric, and that the highly-sensitive capacitance manometers have come to be used in tandem with similarly-constructed manometers designed to function at higher atmospheric-level pressures. The latter expedients involve costs, bulk and complexities which it would of course be advantageous to avoid.